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Taxon Pages
Placopsis imshaugii D. J. Galloway
Nomenclature
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Family: TrapeliaceaeGenus: Placopsis
Media
SUMMARY
Mycobank MB 516034
Thallus rosette-forming, to subirregular, sometimes forming coalescing patches, ±lobate or effigurate at margins, rarely lobate from margins to centre, more commonly areolate centrally, closely attached to substratum from margins to centre, (15–)20–55(–75) mm diam., prothallus absent. Lobes not swollen, rather flattened to subconvex, 0.5–2 (rarely to 4) mm wide, parallel, radiating, contiguous from margins to centre, or only in a broad marginal zone and areolate-cracked centrally, separated by narrow to deep and sometimes gaping cracks; margins entire, flabellate, shallowly rounded or scalloped to occasionally minutely lobulate. Upper surface pale grey brown to pinkish brown at margins, orange-brown to rust-coloured centrally, smooth, subnitid and somewhat coriaceous at or near margins, uneven to minutely papillate to ±cerebriform (10x lens) in central areolae, without isidia, maculae, pruina, pseudocyphellae or soredia. Cephalodia widely scattered centrally, to occasionally developing in groups or clustered in bands towards thallus margins, rounded, 1–5(–9) mm diam., purplish blue when wet, rusty brown to brown-black when dry, shallowly hemispherical to somewhat flattened, margins plicate-crenulate, surface very shallowly ridged at first becoming deeply ridged and/or with gaping, radiating fissures at maturity; cyanobiont in chains, cells rounded to laterally compressed, 5–8.5 µm diam. Apothecia subimmersed to ±aspicilioid at first, becoming sessile and appearing subthelotremoid at maturity, 0.8–1.5(–2.5) mm diam., scattered to crowded centrally, solitary to 2–4-together, rounded to slightly constricted through mutual pressure. Thalline margin prominent, obscuring disc at first, swollen, 0.3–0.6 mm thick, concolorous with thallus or paler, entire to striate-cracked, roughened or wrinkled, without pruina or soredia. Proper margin very thin to scarcely apparent, concolorous with disc or slightly darker; disc deeply urceolate, sometimes reduced to a slit or a pore by the swollen thalline margin, especially when young, yellow-brown to dark-brown, waxy, glossy, epruinose. Epithecium pale pinkish brown, granular, 25–30 µm thick. Hymenium colourless, (200–)250–300 µm tall. Hypothecium pale yellow-brown or pinkish, opaque, 150–200 µm thick. Asci cylindrical, 200–250 x 8–10 µm. Ascospores uniseriate in ascus, broadly ellipsoidal, colourless, 25–30 x 15–18(–20) µm. Pycnidia common, scattered on thallus from near margins to central areolae, immersed, ostiole minute, punctiform, pale whitish to red-brown to black. Conidia filiform, 27–32.5(–35) x 1 µm. Chemistry (J. A. Elix, pers. comm. 2010): medulla K–, C+ red, KC+ red, P–; containing gyrophoric acid (major), lecanoric acid (trace) and atranorin (trace).